diff -r 7f2cd237ee4f -r ec48da635e6c src/Pure/System/isabelle_system.scala
--- a/src/Pure/System/isabelle_system.scala	Thu Jan 09 13:39:33 2020 +0100
+++ b/src/Pure/System/isabelle_system.scala	Thu Jan 09 13:44:16 2020 +0100
@@ -56,8 +56,6 @@
 
   def init(isabelle_root: String = "", cygwin_root: String = ""): Unit = synchronized {
     if (_settings.isEmpty) {
-      import scala.collection.JavaConversions._
-
       val isabelle_root1 =
         bootstrap_directory(isabelle_root, "ISABELLE_ROOT", "isabelle.root", "Isabelle root")